Would You Wash Your Body With Lye?

After spending an afternoon researching soap (totally normal), I came across more than one natural bar that contained lye. Yes, lye is a corrosive substance. And yes, it has also been used to make soap for centuries. But this isn't colonial Williamsburg—I don't churn my own butter or whittle my own furniture. So I wondered if the old-school ingredient, which is also used in hair relaxers, is really considered safe.

Lye, or sodium hydroxide, is a substance that "may generate sufficient heat to ignite combustible material" when in contact with water, and symptoms of exposure include burns, hair loss, and pneumonitis, according to the CDC. That sounds exactly like something I wouldn't want to rub all over my body under a shower. But cosmetic chemist Randy Schueller assured me that only concentrated sodium hydroxide is dangerous, due to a high pH that makes it extremely alkaline. "However, it's perfectly safe when used at low levels in cosmetics, because it's [combined] with acid to form a neutral salt. It's still used in numerous products as a pH-adjusting agent," he says. As far as hair relaxers, Schueller says, ones with lye are "the most effective relaxers, and they are only painful if they are left on the scalp too long. For that reason, they tend to be used in products for professional stylists."

I found lye in hundreds of niche and mainstream body lotions, face serums, sunscreens, shampoos, even mascara, many of which I use daily—though it's most commonly listed as sodium hydroxide. It turns out those colonials were on to something with their soapmaking.